re: Mettler Micro Gram-Atic Balance Alert

[Mark=Linsley%occsafe%sep@sep2.sep.bnl.gov]

I have a copy of a letter from Mettler regarding the Ra sources with lots of 
specific information. In our experiences, this info is NOT 100% accurate, but 
it is pretty good. Here's how it goes;

Anti-static devices in certain Mettler Balances

For a period of time (July 1954 to February 1957 on all models of the B-5 and 
B-6 type and July 1954 to July 1960 on all models of the M-5 type), certain 
Mettler balances were equiped with an anti-static device.

The device is a radium impregnated foil made by the U.S. Radium Corporation 
and sold under the trade name "Ionotron".

The active material incorporated into the foil is Ra-226 in equilibrium with 
all its disintegration products. Ra-226, the parent element in the series of 
materials sealed within the foil matrix, is incorporated as radium sulphate 
in the metal foil matrix. Other materials incorporated into the foil are 
simply gold and silver.

The foil was applied to certain balance parts in the form of small rings 
having an overall diameter of 0.157" (4mm) and an inside diameter of 0.079" 
(2mm). The active material per ring is no more than 3 microcuries.

The listing of balances containing such rings and the location and number of 
rings is given below:

TYPE B, beginning with serial #7500 and ending with -
	serial #14231 on B-5 models
	serial #14491 on B-5 GD models
	serial #15821 on B-6 models

3 rings, located as follows: a) on top of pan brake; b) on sapphire pin, 
release beam, rear right; c) on sapphire pin, release beam, front left.

The use of one ring on the top of the pan brake was started after serial 
#7500 and ended probably before the serial numbers given above. The starting 
and ending serial numbers for this application are not known.

Total per balance, if ring is present on panbrake: 9 microcuries.
Total per balance, if ring is absent from top of pan brake: 6 microcuries.

TYPE M, beginning with serial #5451 to serial #5900, and from serial #17001 
to serial #17677; 7 rings, located as follows: a) one ring on top of pan 
brake; b) one ring each on the 6 sapphire pins of the release beam.
Total per balance: 21 microcuries.

TYPE M, beginning with serial #17678 to serial #105047; 6 rings, located as 
follows: a) one ring each on the 6 sapphire pins of the release beam.
Total per balance: 18 microcuries.

METTLER INSTRUMENT CORPORATION
November 30, 1964

Well, I hope this helps.

Mark E. Linsley
Brookhaven National Laboratory
Safety & Environmental Protection Division
phone: 516-344-3556
email: linsley@mail.sep.bnl.gov